Communication using multiple antennas is efficient to perform high-speed data transmission and to increase the capacity of a communication system. Signal transmission schemes using the multiple antennas may be classified into a beamforming (BF) scheme and a space division multiple access (SDMA) scheme.
In the BF scheme, communication with a mobile station can be performed using a single frequency resource unit, multiple antennas, and an interference cancellation scheme. In the SDMA scheme, simultaneous communication with a plurality of mobile stations can be performed using a single frequency resource unit and multiple antennas at the same point of time.
FIG. 1 illustrates a conventional base station management scheme.
Referring to FIG. 1, conventionally, only one of a beamforming (BF) mode and a space division multiple access (SDMA) mode has to be used as a transmission mode in a cell. The cell can be divided into at least one sector.
When the SDMA mode is used in a cell, a scheduler can select two mobile stations to which a single frequency resource is to be allocated. Although the scheduler may also select three or more mobile stations, it is assumed to select two mobile stations for convenience of explanation. When selecting the two mobile stations, the scheduler has to consider channel orthogonality between the mobile stations.
If the scheduler determines that channels between the two mobile stations are not orthogonal or are nearly non-orthogonal, it is desirable for the scheduler to apply the BF mode to a cell or a sector. A system is assumed in which a cell having three sectors and a base station exists logically or physically in each of the sectors. In this case, the base stations are a short distance away from one another and thus can directly communicate with one another. When the BF mode is applied to the system, a definition has been given for a scheme in which all of the three sectors operate in the BF mode. However, any definition has not been given for a scheme in which the BF mode and the SDMA mode are used together.